1. Field of the Invention
The present invention relates to computer networks and, more particularly, to a repeater unit for use in a Local Area Network operating according to the IEEE 802.3 Standard (an Ethernet network) and which may be expandable to have additional ports, yet operates as a single repeater as defined by IEEE 802.3.
2. Discussion of Related Art
Local Area Networks (LAN) are computer networks which allow a number of data terminal equipment (DTE) to share resources and communicate with each other, thus greatly expanding the usefulness of each DTE. Many types of LANs are known. One common LAN type is a Carrier Sense, Multiple Access Collision Detection (CSMA/CD) network, defined by the IEEE 802.3 Standard and commonly referred to as an Ethernet network. (Ethernet is a registered trademark of the XEROX corporation.) The contents of the IEEE 802.3 Standard are incorporated herein by reference.
Briefly, an Ethernet network operates in the following manner. As seen in FIG. 1, an Ethernet network 100 may include a number of DTEs 102 each connected to a port 103 of a central hub or repeater 104. The DTEs and hub are arranged in a star topology. When a DTE 102 wishes to transmit data to other DTEs on the network, the DTE waits for a quiet period on the network, and then sends the intended message to the repeater 104 in bit-serial form. The repeater 104 then repeats the message to all of the DTEs connected to it. If, after initiating a transmission, another DTE also attempts to transmit a message at the same time, a "collision" is detected. If a collision is detected, then both transmitting stations send a few additional bytes to ensure propagation of the collision throughout the network. The transmitted messages are discarded. The DTEs that attempted to transmit remain silent for a random time ("back-off") before attempting to transmit again. Because each DTE 102 selects its back-off time independently of the other DTEs, a second collision may be avoided.
As seen in FIG. 2, a number of repeaters 104 may be connected to create a series 200 of connected hubs or repeaters. To meet IEEE 802.3 timing requirements, the maximum number of repeaters 104 in any series (from any DTE to any other DTE) is four. Moreover, the star topology allows only one DTE to be connected to each port. Limited port availability on repeaters 104 limits the number of DTEs 102 which may connect to a repeater. The limited number of repeaters in any Ethernet series limits the number of DTEs 102 which may be included in a single Ethernet network series (called a collision domain). If each repeater, for example, has eight ports, only 32 DTEs may be connected to a single collision domain. (Note that FIG. 2 shows a collision domain having 26 DTEs.)
A typical repeater comprises a single integrated circuit chip. Because an IC chip has limited drive current, each chip has a limited number of ports. Thus, each repeater is limited to a number of ports, thus limiting the total number of DTEs which may be connected to a single collision domain. Thus, it is desirable to have repeater units which may be expanded to have additional ports.
Expandable repeaters are known. For example, an expandable repeater is described in U.S. Pat. No. 5,265,123 issued on Nov. 23, 1993 to Vijeh, et al. The contents of this document are incorporated herein by reference. Vijeh, et al. disclose an expandable repeater which connects each repeater unit to an expansion bus. For a repeater unit to transmit on the expansion bus, it must seek permission to do so. An arbiter receives request signals for repeater units seeking to transmit onto the bus, determines which repeater unit may control the expansion bus, issues an acknowledgement signal to that repeater unit, and precludes other repeater units from simultaneously controlling the bus.
U.S. Pat. No. 5,517,520, described above, discloses an expandable repeater in which a number of repeater units are connected in a star topology to an integrator unit. Each repeater unit has an input/output for providing clock, data, control, and collision information to the integrator. A repeater unit issues a request-for-access signal when it wants to transmit to the integrator unit.
It is an object of the present invention to provide an expandable repeater which does not use request or acknowledge signals.